1. Field of the Invention
The present invention concerns an electronic circuit that forms an input interface allowing for the compatibility of ECL or MOS type circuits, made on silicon, with BFL type circuits, for example, made on GaAs or on group III-V materials. This interface circuit is itself made of GaAs and is integrated on the chip of the BFL type circuit for which it forms an input contact.
2. Description of the Prior Art
It is known that the processing of microwave signals calls for the use of digital circuits on GaAs (or other fast materials but GaAs is the most commonly used one) and of digital circuits on silicon. Circuits on GaAs are faster and make it possible to reach frequencies that are not attained by circuits on silicon. However, in the present state of the technology, circuits on silicon are more developed and integrated than GaAs circuits. There is therefore a complementarity between these two types of circuits, but the output levels, in terms of voltages, of the silicon circuits are not directly adapted to the input levels of the GaAs circuits. This is why an interface is necessary.
To illustrate the invention, let us assume that the GaAs circuit has, at input, a BFL (Buffered FET Logic) gate which is well known, supplied for example between V.sub.dd =0 V, V.sub.ss =-5.5 V and with an intermediate voltage V.sub.rr =-3 V. For a gate such as this, the logic levels at inputs and outputs are in the following range: V.sub.high =-2.5 V approximately and V.sub.low =-4.5 V approximately, although the output levels can be shifted by means of shift diodes, depending on the chosen supply voltages.
However, the following are the framing values or limit values of ECL type silicon circuits:
______________________________________ high output level: -1.03 &lt; V.sub.oh &lt; -0.88 low output level: -1.83 &lt; V.sub.ol &lt; -1.62 high input level: -1.1 &lt; V.sub.ih low input level: V.sub.il &lt; -1.5 ______________________________________
and the limits values of CMOS type silicon circuits are:
______________________________________ high output level: -4.9 &lt; V.sub.oh low output level: &lt; V.sub.ol &lt; -0.1 high input level: -3.5 &lt; V.sub.ih low input level: V.sub.il &lt; -1.5 ______________________________________